In the field of data communication between and among various digital machines traditionally, such machines are linked with wire, coaxial cable, optical cable and the like. The communication link between machines has tied the machine to a particular location such as the user's desk. Even with an aimed infrared link such as disclosed in U.S. Pat. No. 4,977,618 a computer must be hardwired to the infrared transceiver and essentially immobile.
With the advent of portable and notebook computers and availability of application software, users want the power of a network without being chained to their desk. Such a user includes a corporate employee and student. In the corporate environment the user will produce their work product on their notebook computer. Additionally, fellow employees will attempt to communicate with the user via electronic mail over a local area network. Accordingly, the user desires to carry his notebook with him throughout the corporation for example, to meetings, to a laboratory, to seminars and the like. The user will want to access data or provide data to fellow workers at meetings, lectures and the like as well as take notes, compile data, prepare memos, annotate documents and be able to access the network while doing so.
A student will move from classroom to classroom, to the library, to laboratories and other similar locations with their notebook. Ideally, a student would receive an assignment via the network, prepare the assignment on their notebook computer and return the assignment via the network for grading. Tests could be similarly administered. The immobility of a node on a traditional network severely restricts the power of a portable by either preventing portability or when portable preventing access to a network.
Information has been transmitted via radio signals. A radio transceiver would allow a user mobile access to a local area network. However, radio is subject to rigorous control by the Federal Communications Commission making this approach prohibitively expensive. Further, the information transmitted over or stored on a radio local area network is vulnerable to intentional or inadvertent corruption or theft.
Another approach using diffuse infrared signals, allows a user mobility within a given chamber. A transponder is incorporated in a ceiling or wall of this technique. Multiple transponders are also contemplated for chambers too large to be efficiently covered by a single transponder. Those multiple transponders are connected together by signal cables. By requiring the transponders to be connected by wire the same difficulty and problems associated with forming cable connections are incurred as for an ordinary link such as a local area network. Such a system only allows node to node communication via the ceiling transponder. No direct node to node communication is possible. Thus, every room within a facility would be required to have a transponder for communication. No communication would be possible unless a transponder were present. Further, a protocol or architecture for data communication allowing true user mobility has never been achieved.